Peace Status Keeps Changing

Game 1068930

Germany (me) and others have been at war with Italy (inactive player) and reduced it to one province, the island of Ponte Delgada.

I keep setting my diplomatic status to Peace but after a while it changes back to War. I have not made any attacks on Italy or Italian units for several days now: I was expecting Italy to follow suit eventually and change its diplomatic status to Peace as well.

Instead my own status keeps changing every few hours to War, is there a reason for this?